Hemlocks are a very stable tree once they are established in your landscape. After the initial installation adequate water is essential for not only establishment but also continued growth and development. Initially water ~ 10 gals per week. Do not allow the roots to dry out BUT do not overwater. Once established (2-3 months), water with at least 5 gals. per week. If temperatures are over 90o then water 2x per week. 1″ of rainfall is equivalent to ~ 5 gals. of water. Place a rain gauge near the trees and monitor rainfall and adjust watering as needed. Needle drop occurs when the trees are in extreme drought stress. Many times the needle drop is identified as mite or disease activity but a simple inspection of the soil to check moisture will confirm the drought conditions. The needle drop is usually permanent due to the damaged roots. Hemlocks also are susceptible to spider mites, especially when stressed. SPIDER MITES: Keeping the trees out of water stress reduces their susceptibility to mites. If the hemlocks become infested appropriate applications of miticides will control the problem. HEMLOCK WOOLY ADELGID: The Hemlock wooly adelgid is a relatively new pest of the Hemlocks. This pest can kill entire trees if left untreated. At this time this pest is located in North Georgia and further north but has not been found in Atlanta.
An excellent site for information on how to treat the Hemlock Wooly Adelgid can be found here.
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